This investigation will determine the timing and the clinical and biological significance of brain atrophy and white matter lesions seen in magnetic resonance imaging (MRI) of patients with human immunodeficiency virus (HIV). This study is part of an ongoing investigation at the HIV Center for Behavioral and Clinical Studies at the New York State Psychiatric Institute which examines the natural history and evolution of neurological and neuropsychological manifestations of HIV infection in gay men and parenteral drug abusers of both sexes. The primary objective of this new investigation is to determine the relationship of abnormalities on MRI to the prevalence, progression and incidence of neuropsychological, neurological, and virological parameters of disease in cerebrospinal fluid (CSF). We hypothesize that MRI will reveal the earliest signs of central nervous system infection by HIV. Atrophy and white matter lesions will precede or occur simultaneously with neurological and neuropsychological changes and will correlate with virological evidence of infection in CSF. A representative sample of the cohort being investigated for natural history of HIV will have MRI on an annual basis and a subsample will have CSF examinations to determine the psychobiological correlated of the radiological manifestations. Over four years we intend to determine the prevalence and incidence of MRI abnormalities in gay men and parenteral drug abusers who are HIV positive, determine the psychobiological correlates of these lesions, determine the virological parameters in CSF and determine their relationship to the HIV Center at the New York State Psychiatric Institutes, we will also examine the relationship to other aspects being investigated there, such as psychopathology, sexual behavior and immune status.